High frequency smelting furnace



Dec. 26, 1939; F. HARTMANN HIGH FREQUENCY SMELTING FURNACE Filed Nov.17, '1938 Patented Dec. 26, 19 39 HIGH FREQUENCY SMELTING FURNACE FritzHartmanm-Dortmund, Germany, assignor to Kohle-und Eisentorschung G.-m.b. 11., Dusseldon, Germany, a limited-liability company ApplicationNovember 17, 1938, Serial No. 249,930 In Germany November 19, 1937 4Claims; (Cl. 13-27) To counteract the danger of breaking out, it and'theoutflow temperature of the water can be 20 is proposed according to theinvention to utilize read at any time. The interposing of a secondarythe change of temperature of the cooling water, circuit 8 is recommendedas the thermo-currents caused by the penetration of the hot metal intoare too weak to attain the direct actuation of the the wall of thecrucible, by arranging in the main switch.

cooling water current temperature-influenced Instead 'of the thermoelectric couple 3, other 26 devices, such as thermo-electric couples,redevices may be fitted according to the invention sistance coils orbimetal strips, which in the provided they canbe influenced by changesin event of inadmissible rise in temperature cut temperature. Forexample a resistance coil may out the furnace switch by means of knownmebe provided which presents the advantage that 30 chanical orelectrical transmission elements. It an intermediate relay betweenresistance coil 30 is advisable to arrange a thermo-electric couple andcut out of the main switch can be dispensed or the like not only at thecooling water outlet with. Thermometers with cut off contacts may butalso at the cooling water inlet. Thus, it is also be employed. By usingbimetal strips as possible to control the actual rise intemperatemperature influenced devices a mechanical 5 ture of the coolingwater in the furnace indetransmission of the movement of the bimetalpendently of the inlet temperature of the coolstrip under changes oftemperature to the main ing water which mostly fluctuates. If the twoswitch may also be attained. thermo-electric couples in differentialconnec- According to Fig. 2 thermo-electric couples are tion are jointlyactuated, even a considerable inarranged one 6' in the outlet 6 andanother 6 crease in the sensitivity of the cut out canv be in the inlet3 for the cooling water. The two 40 thereby attained so that it. ispossible to indicate thermo-currents, in the case of differentialconbreaking out in its inception. nection, indicate the difference inthe tempera- Two embodiments of the invention are illustures of thecooling water at the inlet and outlet trated by way of example in theaccompanying points. By the diiferential connection on the drawing, inwhich:-- electromagnet 'l the protecting arrangement is 45 Fig. 1 is adiagrammaticalview showing the rendered independent of temperaturefluctuations arrangement of a thermo-electric couple in the of theinflowing cooling water. Furthermore, by cooling water inlet, thedifferential connection the sensitivity of the Fig. 2 is a similar viewshowing the arrangeindication or of the adjustment of the cut out mentof a thermo-electric couple in the inlet point of the main switch canbeconsiderably in- 60 and another in the outlet of the cooling water.creased. This is perhaps advantageous for show- In the drawing ldesignates a crucible in ing on an indicating instrument the relativelywhose wall a current conducting coil 2 is em slight increase intemperature already at the bedded and is connected to asource' 9' ofhigh beginning of a break out. The protecting arfrequency alternatingcurrent through the con- When smelting metals in high-frequency furnacesof large capacity there exists, owing to the relatively thin walls ofthe crucible, the danger of the liquid metal breaking out through thecrucible wall. In the case of such breaking out, apart from thedestruction of the coils, explosions might occur, and the liquid metalmay come into contact with the cooling water.

Experience has shown; that a breaking out is preparcd'by the formationof small cracks or crevices in the crucible wall which cracks andcrevices flll with metal and spread in outward direction. It is evidentthat such cracks cannot be detected during the smelting.

In most cases the breaking outtakes place so suddenly that, even if thethreatening breaking out canmake itself apparent in some way by externalsigns, there is nevertheless not enough time to cut out the furnace.

tacts II and II. In the example illustrated the coil consists of a tube,through which the cooling water flows. The cooling water enters at 3 andpasses out at 4. The electric connection of the induction furnace iseffected in the usual 5 manner over fuses ill and a main switch 5.According to Fig. 1 the protecting device consists of a thermo-electriccouple 6 which acts on a relay I. The relay 1 in responding, closes asecondary circuit 8 to energize an electromagnet 10 I l to attract adetent armature l5 by which the main switch 5 is switched ofi throughthe action of a spring i6.

An indicating instrument may be used instead of the relay I, if thisinstrument has in known manner cut off contacts by which the secondarycircuit 8 is controlled. The use of an indicating instrument instead ofa relay presents the advantage that the heating process can be observedrangement cuts out the furnace only when the difl'erence in temperatureof the water at the inlet and outlet points increases. In most casesthis will take place only when the metal breaking out is already nearthe coil whereby electromagnet I will be energized sufiiciently toattract its armature I! for closing the secondary circuit 8, as in thepreviously described embodiment, to actuate switch 5 through the releaseof detent :2 by electromagnet M and the action of spring I claim:

1. In a high frequency smelting furnace, means for avoiding breakingthrough, comprising in combination with a crucible and an electriccircuit for heating said crucible, a main switch in said circuit, acooling water conduit surrounding said crucible, at least one heatinfluenced device inserted in the cooling water, arranged in saidcircuit and influenced by an excessive rise in temperature in thecooling water circulating through said conduit, and transmissionelements between said device and switch and adapted to cut out saidcircuit through the actuation of said switch at the influencing of saiddevice, by an excessive rise in temperature in the cooling water.

2. In a high frequency smelting furnace of the nature'set forth in claim1, two heat influenced devices in the circuit, a difierential relayconnected to both of said devices and cooperatively connected to themain switch.

3. In a high frequency smelting furnace, means for avoiding breakingthrough, comprising in combination with a crucible and an electriccircuit for heating said crucible, a main switch in said circuit, acooling water conduit surrounding said crucible and connected with saidcircuit to constitute the induction heating coil of the furnace, atleast one heat influenced device inserted in the cooling water, arrangedin said circuit and influenced by an excessive rise in temperature inthe cooling water circulating through said con- I

